Electrical

ME218B Final Project Schematic.pdf

The Schematic

Overview

NORMAN's brain consists of two PIC32 microcontrollers, one acting as the leader, and the other acting as the follower. The follower receives information from the outside world, and the follower acts on that information. The two microcontrollers' responsibilities are as follows:

Leader:

Servos
Drivetrain
LEDs

Follower:

IR Sensor
Tape Sensors

Leader

Leader PIC32

The leader PIC acts on information it receives from the follower. We programmed the PIC using a SNAP Programmer in the configuration (shown to the right).

Servos

Three servos make NORMAN's efficiency and expressiveness possible.

The arm servo is a DS3235 35 kg servo motor, capable of lifting crates of coal towards the desired bucket.

The coal paddle servo, a micro servo, pushes the coal into NORMAN's crate

The flag raise servo raises a blue or green flag, depending on which side of the arena NORMAN is placed.

Drivetrain Motors, Motor Drivers, and Encoders

We used TLE-5206 H-Bridges to drive our motors, with capacitors for filtering noise. Each motor required a separate H-Bridge.

We mounted encoders and magnets to the back ends of the motors to track their rotation.

Neopixel LEDs

Neopixels use SPI, which allowed us to use a single output pin on our leader microcontroller for all 40 of the LEDs. These neopixels have 3 pins: +5V, GND, and Data.

Follower

Follower PIC32

The follower PIC sends information it receives to the follower using SPI. We programmed the PIC using a SNAP Programmer in the configuration (shown to the right).

IR Beacon Sensor

The IR beacon sensor consists of a transresistive amplifier and a Schmitt trigger, separated by a high-pass filter, a non-inverting op amp with gain, and a low pass filter. A unity gain buffer provides a 2.5V reference voltage to the low- and high-pass filters.

Tape Sensors

NORMAN has 5 tape sensors (IR emitter and receiver pairs), which it uses as a means of detecting black tape on the arena. Three of the sensors are located at the front of the robot, and two are directly underneath the wheel axle.

The image below shows the underside of NORMAN with its full tape sensor layout

Power Distribution Board

Special thanks to the teaching team for developing the Power Distribution Board (PDB) printed circuit board. The link to the PDB Github can be found here.
The PDB allowed us to connect our 2 7V batteries in series, along with a main power switch and a fuse.The bottom row of screw terminals supplied power to our motors.

Calculations

To design an IR sensor capable of detecting pulsing frequencies coming from different locations in the arena, we designed a circuit that converts the incident light on a phototransistor into a digital output for the microcontroller to read. This involved calculating cutoff frequencies for low- and high-pass filters, to remove any low- and high-frequency noise (i.e. DC offset caused by sunlight and other noise from our wires and protoboard).We calculated the cutoff frequency using the following equation:

Since the lowest and highest beacon frequencies in the arena are 909 Hz and 3333 Hz, we designed the beacon detector with a high-pass filter cutoff frequency of ~600 Hz, and a low-pass filter cutoff frequency of ~4000 Hz. We made a simple spreadsheet for these calculations (see below).

Low-Pass Filter

High-Pass Filter

PIC Layout

To keep track of all of the available PIC32 pins and their corresponding port names and other important information about them (5V tolerant, analog capable, etc.), we made the following spreadsheet.

Electronics Bill of Materials

Note: The total price reflects the commercial value of all components. Since some parts were included in our course lab kits, the actual cost incurred by the team was lower than the expected cost to reproduce NORMAN. AMPS, Lab64, and SPDL are all Makerspaces/Labs at Stanford.

Total Electronics Hardware Cost: $37.39

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